It is known that intumescent materials have a flame-retardant effect by foaming when strongly heated, e.g. in the presence of a fire, to form an insulating layer which does not burn lightly and in this way suppress, inter alia, the dripping of molten, possibly burning material.
Intumescent metal-containing melamine phosphates are already known from EP 2 183 314 B1. However, these have the disadvantage of a lack of thermal stability. Thus, for example, the aluminum salt [(Mel-H)]3(+)[Al(HPO4)3](3−) described there gives off one mole of melamine and two moles of water under thermal treatment at 280 to 300° C., forming [(Mel-H)]2(+)[AlP3O10](2−). A similar situation applies to [(Mel-H)]2(+)[MgP2O7](2−). Furthermore, the products described there can be obtained only in a multistage process. These compounds also all have a disadvantageous modulus (melamine/metal ratio) of 3 or 2.
Amine metal phosphates are likewise known, as described, for example, in Inorg. Chem., 2005, 44, 658-665, and Crystal Growth and Design, 2002, 2(6), 665-673, but owing to their alkylamine content they have an unsatisfactory thermal stability and are therefore not suitable as flame retardants.
Cyanoguanidine (dicyandiamide) zinc phosphite is described in Inorg. Chem., 2001, 40, 895-899, where the modulus (cyanoguanidine/zinc ratio) is 1. Guanidine zinc phosphates are not to be found in this publication. Aminoguanidine zinc phosphite is described in Intern. J. of Inorg. Mater., 2001, 3, 1033-1038, where the modulus (aminoguanidine/zinc ratio) is 2:3. The synthesis is likewise carried out hydrothermally. Aminoguanidine zinc phosphates are not to be found in this document. A guanidine zinc phosphite is disclosed in JCS Dalton Trans. 2001, 2459-2461, where the modulus (guanidine/zinc ratio) is 2. Guanidine zinc phosphates having a modulus of 1 are not described.
Guanidine zinc phosphates are also disclosed in Chem. Mater., 1997, 9, 1837-1846. However, these are prepared hydrothermally and additionally require long reaction times. In addition, these phosphates have a modulus (guanidine/zinc ratio) of 0.5, 2 and 3 and are therefore distinctly different from the azine metal phosphates of the invention, which all have a modulus of 1.
Metal-free intumescent melamine phosphates are likewise known. Thus, a number of processes for preparing melamine polyphosphates have been described, for example in WO 00/02869, EP 1 789 475, WO 97/44377 and EP 0 974 588. However, preparation according to these processes is time-consuming and the processes are associated with a very high energy consumption because of the high reaction temperatures (340 to 400° C.). In addition, urea is used as further additive.
A melamine polyphosphate-based formulation which is already on the market is described in EP 1 537 173 B1.
In addition, there are already intumescent flame retardant systems which are based on melamine, e.g. on melamine salts of 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]-undecane 3,9-dioxide (MAP) and on melamine salts of bis(1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octan-4-ylmethanol) phosphate (melabis).
Further intumescent systems are described in chapter 6, pages 129-162 “Fire Retardancy of Polymeric Materials”, 2nd edition (2010), editors: C. Wilkie, A. B. Morgan, CRS Press, FL, USA.
Flame retardants for polyamides (PA) and thermoplastic polyesters (PET/PBT) are described in detail in chapters 5 and 6, pages 85-119, “Flame Retardants for Plastics and Textiles”, (2009), authors: E. Weil and S. Levchik, Hanser Verlag, Munich.
However, the flame retardants described in the prior art have the disadvantage that they frequently have an unsatisfactory flame retardant effect and are unsuitable, or have only limited suitability, for use in plastics, in particular thermoplastic plastics and elastomers in the electrical and electronics sector. In addition, some phosphorus-containing flame retardants influence the electrical conductivity and can thus, for example, have an adverse effect on the properties of a thermoplastic plastics provided with flame retardants in electrical components.
Despite the numerous publications known from the prior art, there continues to be a need for flame retardants having optimized properties and improved environmental compatibility.
It was therefore an object of the present invention to provide more effective flame retardants, in particular ones having improved secondary properties such as reduced acidity (higher pH values) and thereby a lower corrosivity and also lower conductivity, compared to the flame retardants known from the prior art.
In particular, it was an object of the present invention to provide flame retardants which have a high degree of intrinsic (thermal) stability and give a polymer excellent mechanical properties after incorporation of the flame retardant.
It is therefore an object of the present invention to provide such flame retardants. These should also be readily obtainable.